Abstraction for spec worker and code cleanup (#11643)

python/sglang/srt/speculative/eagle_info.py

@@ -574,6 +574,9 @@ class EagleVerifyInput(SpecInput, EagleVerifyInputV2Mixin):
 
 @dataclass
 class EagleDraftInput(SpecInput, EagleDraftInputV2Mixin):
+    # Constant: alloc length per decode step
+    ALLOC_LEN_PER_DECODE: ClassVar[int] = None
+
     # The inputs for decode
     # shape: (b, topk)
     topk_p: torch.Tensor = None
@@ -609,9 +612,6 @@ class EagleDraftInput(SpecInput, EagleDraftInputV2Mixin):
     new_seq_lens: Optional[torch.Tensor] = None
     verify_done: Optional[torch.cuda.Event] = None
 
-    # FIXME(lsyin): remove this hack
-    ALLOC_LEN_PER_DECODE: ClassVar[int] = None
-
     def __post_init__(self):
         super().__init__(SpecInputType.EAGLE_DRAFT)